Studies on Aging of the Bronchial Trees and the Bronchial Vascular System

3. Effect of Age on Intrinsic Regulatory Mechanism between Bronchial Trees and Bronchial Vascular System

Abstract

The present experiment was conducted in thirty dogs to investigate effect of age on intrinsic regulatory mechanism which was proposed to be present between bronchial trees and bronchial vascular system. Changes in bronchial muscular reactivity and bronchial vascular tone to the administration of serotonin, acetylcholine and adrenaline in small doses were tested simultaneously by the method described in previous reports and the result was compared between the young and the old group.
Serotonin and acetylcholine caused bronchial arterial dilatation as well as bronchoconstriction, while adrenaline injected directly into bronchial artery resulted in bronchial arterial constriction and bronchodilation.
The young and the old group showed essentially same mode of reaction to each drug and changes in bronchial vascular system in relation to variable bronchial muscular tone were not significantly different. The reversed reaction in air ways and bronchial arteries to the administration of these drugs might be reasonably explained by the proposed intrinsic regulatory mechanism between two systems, which would enhance bronchial arterial dilatation to allow increase of flow in accordance with bronchial constriction.
The effect of age on this mechanism, as disclosed in the present investigation, seemed to be insignificant.
Physiological and morphological changes of the air ways in the old group were certainly far beyond the extent that could be expected from concomitant changes in bronchial vascular system.
This result has suggested the assumption that chronic irritation of air ways due to continious exposure to external environment should play more important role than physiological aging in establishing such a remarkable changes in the air way.